1. Field of the Invention
This invention relates to a temperature controller apparatus and, more particularly, to such apparatus which provides multiple back-up modes in the event of a detected failure or failures for use with a temperature chamber.
2. Description of the Prior Art
In the prior art, temperature chambers, which may be used as refrigeration units, for example, in trucks, railroad cars or the like, to temporarily store perishable food goods while being transported to a desired destination, typically include a chamber which may have an insulated outer shell, a thermostatically controlled valve and one or more canisters having a supply of coolant contained therein. In such temperature chambers, the flow of coolant into the chamber is regulated by the control valve. That is, the thermostatically controlled valve monitors the temperature inside the chamber and, when the inside temperature rises above a predetermined set temperature, the control valve opens so as to allow the coolant to flow into the chamber, thereby lowering the inside temperature. The valve typically remains open until the inside temperature is reduced below the predetermined set temperature. A temperature probe, which is coupled to the control valve, may be utilized to enable an indication of the temperature at a particular location inside the chamber to be supplied to the control valve.
However, as is to be appreciated, a single temperature probe may not provide a reliable indication of the temperature inside the chamber. That is, depending on the location of the temperature probe inside the chamber, the probe may "sense" a temperature which is different than a temperature at other locations within the chamber. This may be due to the conventional positioning of the temperature probe proximate to the inlet of coolant flow into the chamber.
To provide a more accurate temperature value, multiple temperature probes which are located at respective locations inside the chamber may be utilized. In this situation, the temperature values from the probes are averaged and the averaged temperature is utilized to control the valve. However, if one or more of the multiple probes become defective or inoperative, the temperature obtained therefrom, even though it is erroneous, may still be utilized in computing the average temperature and supplied to the control valve. As a result, the flow of coolant into the chamber may be improperly regulated, thereby causing the inside chamber temperature to be improperly controlled. As is to be appreciated, this may damage the perishable food goods or other items contained within the temperature chamber.
Such problems also exist when the temperature chamber controls the temperature inside the chamber at relatively high temperature values. As is to be appreciated, in this situation, the temperature chamber includes a heat source whose operation is regulated so as to control the chamber temperature.
The prior art has therefore failed to provide a means for receiving temperature information from a plurality of temperature probes provided in such a temperature chamber and for providing therefrom a reliable temperature control signal for supply to a control valve or other similar device which, in turn, controls the temperature inside the temperature chamber even when one or more of the temperature probes are inoperative.